1. Field of the Invention
The present invention relates to a vehicle navigation device that guides a vehicle to a destination according to a guidance route. More particularly, the invention relates to a vehicle navigation device having the function of displaying on a map screen of a display not only the guidance route, but also information indicative of points of interest (hereinafter referred to as “POI”) which serve as landmarks near the route.
For convenience, the information indicating the POI will be referred to as the “landmark” below. Unless otherwise specified, the “vehicle” means a car.
2. Description of the Related Art
A known typical vehicle navigation device comprises a map data storage unit for prestoring map data, such as a CD-ROM, a DVD-ROM or an IC memory card, a display unit, a GPS (Global Positioning System) receiver, and a sensor for detecting a present position and a present direction of a vehicle, such as a gyro, a vehicle speed sensor, or the like. The navigation device is designed to read map data for the area including the present vehicle position from the map data storage unit, and then to draw a map image covering the vehicle position and its surroundings on a screen of the display unit based on this map data, while superimposing a vehicle position mark (location) on the map image displayed on the screen. Such a navigation device scrolls the map image as the vehicle travels, or moves the vehicle position mark with the map image fixed on the screen, thereby enabling a user to understand at a glance where the vehicle is now traveling.
Generally, the vehicle navigation device has the function of guiding the user (route guidance function) to a desired destination so that he/she can easily travel to the destination without taking a wrong path. This route guidance function executes an automatic route search for an optimal route (typically, the lowest cost route) connecting a starting point (in most cases, the present vehicle position) to the destination by making a simulation calculation such as a horizontal search method or Dijkstra's algorithm method using the map data, and storing the route searched for or found as a guidance route. During the vehicle travel, the guidance route found is displayed on the map image in a different and distinguishable form (for example, in a different color, or in a thicker line) from the other roads. When the vehicle approaches a predetermined distance to an intersection where the vehicle is to turn on the guidance route, the guidance function displays a guidance view of the intersection superimposed on the map image (which view includes an enlarged diagram of the intersection and an arrow for designating a recommended traveling direction at the intersection), thus enabling the user to recognize the optimal route to the destination.
Particularly, when searching for the route, the navigation device needs the user to preset the destination, or if necessary, a way point to the destination (that is, which route the user desires to pass through to reach the destination). Under certain circumstances, various criteria (for example, whether the user gives a high priority to a toll road or a general road, or whether the user wishes to reduce the traveling distance or the traveling duration) also should be set. Based on this preset data, the navigation device searches for a plurality of possible routes to the destination to display these searched routes, for example in respective different colors, and subsequently conducts the route guidance as mentioned above in compliance with one of these routes selected by the user.
Such known navigation devices display the optimal guidance route determined from a result of the aforesaid route search superimposed on a map screen of the display, while displaying on the map screen the POI information serving as landmarks on the guidance route, such as a convenience store, a bank, a gas station and the like. With the guidance route to the destination shown, the display of the POI information as the landmarks for specifying the guidance route facilitates the user's confirmation of the route during the vehicle travel.
In the prior art, however, the POI information displayed with the guidance route included only fixed contents that had been prestored in a memory of the device or the like. That is, only POI information is displayed that has been included in the map data from the beginning when a disc such as the CD-ROM, the DVD-ROM, or the like was manufactured for storing the map data.
As described above, in the known vehicle navigation devices, the POI information displayed when the route guidance is shown or executed on the map screen of the display has only the fixed or limited contents included in the map data prestored in the CD-ROM and the like. Thus, even if POI information on the points of interest serving as the landmarks displayed on the map screen has been updated by the user's settings, this updated POI information cannot be reflected on the actual map screen.
For instance, suppose that when displaying POI information on the convenience stores located near the guidance route being shown or displayed, the number of the convenience stores increases or decreases, because new ones are opening or because some stores are lost due to bankruptcy or a shift to other business. In these cases, since the POI information capable of being displayed is limited to only the fixed information prestored in the CD-ROM and the like, the navigation device fails to display the current POI information reflecting the increase or decrease in the number of stores on the map screen.
In other words, even when the POI information about the points of interest serving as the landmarks to be displayed has been updated, the updated POI information, namely the updated part of the information, cannot be displayed on the map screen. Therefore, the points or facilities actually existing around the guidance route to the destination do not match the corresponding POI information being displayed on the map screen, which information pertains to the points not updated. This mismatch undesirably makes it difficult for the user (generally, a driver) to identify or recognize the actual or true guidance route by referring to the displayed POI information as landmarks.
As mentioned above, the POI information displayed on the map screen does not necessarily correspond to the actual points of interest. This inaccurate POI information cannot be used with accuracy as landmarks in order for the user or driver to identify the actual or existing guidance route. Additionally, looking at the map image including this incorrect POI information frequently results in interruption of the user's driving